1. Field of the Invention
This invention relates in general to magnetic flux sensing apparatus and, in particular, to a magnetic head of the type employing a thin single domain magnetic film structure as a magnetoresistive element responsive to the flux being sensed.
2. Background Relative to the Prior Art
Playback of recorded signals from a magnetic recording medium by means of a conventional magnetic head that is sensitive to flux rate-of-change is difficult for low recorded signal frequencies, and theoretically impossible for recorded DC signals, or when there is no relative speed between the recording medium and the magnetic head. Accordingly, various techniques have been proposed for sensing magnetic flux, as opposed to the rate-of-change of such flux, e.g. Hall effect, flux gate, and magnetoresistive devices, thereby to permit recording media to be used as optimally as possible.
With regard to the matter of magnetoresistive devices for sensing magnetic fields, the use of a thin single domain magnetic film for field sensing purposes is known. Representative prior art depicting the use of magnetoresistive thin film structures can be found in the following references: U.S. Pat. No. 3,731,007; U.S. Pat. No. 3,947,889; U.S. Pat. No. 3,921,218; U.S. Pat. No. 3,945,038; and U.S. Pat. No. 4,051,542. Typically, a thin (planar) single domain magnetoresistive film is employed to sense a magnetic field to which it is exposed by passing an electrical/sense current (either AC or DC) through the film, the film magnetization vector being canted with respect to the direction of current flow. The field being sensed exerts a torque on the magnetic moment in the film, causing the resistance of the film to increase or decrease depending on the sense and magnitude of the field applied to the film. The resistance of the film is, therefore, the analog of the field strength. Although such use of a magnetoresistive film represents a reasonably workable technique in the art of magnetic flux sensing, it suffers from, among other things, the standpoint of reduced sensitivity to the external field: this is because pole formation at the edges of the film in question causes the generation of a large demagnetization field which adversely affects the effectiveness of the film.